Skin storage system

ABSTRACT

A method and means for preparing large cellular skin patches for preservation for cyrogenic storage and subsequent thawing which comprises applying a woven scrim to one side of a large patch of cellular skin, with the scrim having a generally open and reticulate pattern of less than about 64 openings per square inch, and thereafter freezing the skin patch for cyrogenic preservation. Large cellular skin patches are normally stored by rolling the patch prior to freezing, and for thawing, the fluid being used gains ingress to the zones between adjacent rolled layers through the reticulate pattern of the interposed scrim.

United States Patent [191 Beisang et al.

1451 Feb. 19, 1974 SKIN STORAGE SYSTEM [73] Assignee: GeneticLaboratories, Inc.,

Roseville, Minn.

[22] Filed: Oct. 27, 1972 [21] Appl. No.: 301,426

52 u.s.c1 ..156/80,128/1R,128/305.5, 156/498, 161/89 51 Int. C1,. l}29c27400 58 FieldofSearch ..156/80,282,31'1','498; 161/89, 92, 151; 128/1R, 305.5; 195/1.7

[56] References Cited UNITED STATES PATENTS 2,583,341 l/l952 Resse128/3055 Primary Examiner-George F. Lesmes Assistant Examiner-James J.Bell [57] V ABSTRACT A method and means for preparing large cellularskin patches for preservation for cyrogenic storage and subsequentthawing which comprises applying a woven scrim to one side of a largepatch of cellular skin, with the scrim having a generally open andreticulate pattern of less than about 64 openings per square inch, andthereafter freezing the skin patch for cyrogenic preservation. Largecellular skin patches are normally stored by rolling the patch prior tofreezing, and for thawing, the fluid being used gains ingress to thezones between adjacent rolled layers through the reticulate pattern ofthe interposed scrim.

6 Claims, N0 Drawings SKIN STORAGE SYSTEM BACKGROUND OF THE INVENTIONThe present invention relates generally to an improved means and conceptfor preparing large cellular skin patches for preservation by cryogenicstorage, and more specifically to a method and means for preparing suchpatches through the application of a layer of woven scrim to one side ofthe patch prior to rolling, cryogenic freezing and storage.

Large cellular skin patches are used for medical purposes in relativelylarge quantity, these patches being utilized for treatment of patientssuffering from loss of skin due to a variety of causes such as, forexample, burns, brasions, or the like. Skin grafting techniques havebeen found to aid patients toward ultimate recovery. The cellular skinis obtained from swine, human cadavers, or natural donors. Accordingly,the size of the individual patch will frequently be limited and in orderto overcome the size limitation, the individual small patches may besecured together to obtain relatively large patches or sheets.

In the event fresh skin is utilized, its shelf-life is quite limited,normally being less than about days. It has been found that skin may becryogenically preserved for relatively extended periods of time, andthawed immediately prior to use. One of the disadvantages from thecryogenic preservation is that the skin suffers damage whenever thethawing time is greater than approximately one minute. If the thawingtime can be rendered rapid, that is, less than one minute, the skin willbe essentially as acceptable as freshly obtained skin. The presentinvention provides a system for cryogenically preserving skin andarranging for rapid thawing of the cryogenically preserved skin.

SUMMARY OF THE INVENTION In accordance with the present invention,stated briefly, the individual patches are preferably coupled togetherto form relatively large sheets of skin, with these sheets beingprovided with a scrim backing. The scrim has a generally open andreticulate pattern with less than about 64 openings per square inch,thus providing a regular spacing between the surfaces of mutuallyadjacently disposed layers of rolled sheet, with this spacing permittingease of ingress to the contacting fluid used for thawing the materialprior to use. The scrim is preferably fabricated from nylon orpolyethylene terephthalate threads, these threads being generallynon-hygroscopic in nature and hence useful for contact with thawingfluids such as saline solutions or the like.

Thus, the concept involves the initial preparation of large patches orsheets of cellular skin, with these patches being provided with a wovenscrim backing, preferably adhesively secured or applied to the skinsurface. Thereafter, the scrim-backed material is sterilized, rolled forstorage, and cryogenically frozen. The cryogenically frozen material canbe retained until required for use, at which time it is thawed andapplied to a patient where indicated.

Therefore, it is a primary object of the present invention to provide animproved method and means for preparing relatively large cellular skinpatches for preservation by cryogenic storage and subsequent thawingwhich comprises applying the woven scrim to one side of a large patch ofcellular skin prior to cryogenic freezrng.

It is yet a further object of the present invention to provide animproved method and means for preparing large cellular skin patches forpreservation for cryogenic storage wherein the patches are provided witha backing of a woven scrim having a generally open and reticulatepattern with less than about 64 openings per square inch.

It is yet a further object of the present invention to provide animproved method for preparing large cellular skin patches forpreservation by cryogenic storage wherein the patches are provided witha woven scrim backing with relatively large openings in the backing, andwherein the scrim is prepared from nonhygroscopic threadsof syntheticresin such as nylon or the like.

Other and further objects of the present invention will become apparentto those skilled in the art upon a study of the following specificationand appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the preferredembodiment of the present invention, a method and means for preparinglarge cellular skin patches or sheets for preservation by cryogenicstorage and subsequent thawing is provided. Specifically, these patchesare obtained by suitable extraction from swine, human cadavers, ordonors, with the size of the individual patches normally being somewhatlimited. For normal medical procedures, the large patches or sheetswhich are preserved for subsequent use are normally of a size of l0-l5inches. These individual sheets may comprise several individual patchessecured together by sewing along the edges or by adhesive bondingtechniques. When adhesives are employed, one suitable adhesive isiso-fluoro cyanoacrylate, which is a normally commercially availableadhesive. Other cyanoacrylates may be employed, specifically thosehaving received approval for such use.

The individual large patches or sheets are then treated so as to apply awoven scrim to one side of the patch, with the woven scrim being onewith a generally reticulate pattern, preferably having less than about64 openings per square inch. Such a loose weave is desirable in order topermit ease of ingress of the contact solution being used for thawingpurposes, and to prevent or limit surface-to-surface contact zones withthe skin. The adhesive employed to bond the scrim to the skin ispreferably one of approved formulation, such as, for example, theiso-fluoroyanoacrylate previously discussed.

It will be further appreciated that the term woven Y ble of withstandingexposure to normal saline solutions. In this connection, nylon orpolyethylene terephthalate hygroscopic and accordingly are capable ofwithstanding exposure to the saline solutions employed for achievingrapid thawing of the cryogenically preserved material.

For cryogenic preservation, the substance is exposed to cryogenictemperatures in the range of from between about 70 C. and lower. Suchcryogenic storage facilities are, of course, available commercially.

In order to provide appropriate sterilization of the skin and appliedscrim, exposure to the standard ethylene oxide environments arepreferred. Such sterilization facilities are likewise commerciallyavailable and widely practiced in the art at this time.

The individual cryogenically preserved cellular skin patches or sheetsare preferably in a substantially hermetic enclosure, although, ifdesired, standard film envelope receptacles may be utilized.

For thawing, the previously prepared and cryogenically preservedcellular skin patches or sheets are immersed in a relatively large tankof normal saline solution. The volume of the tank will be sufficientlylarge so as to accommodate the rapid thaw of the cellular skin patch orsheet without suffering from a significant drop in temperature. The skinpatch or sheet is brought to room temperature in a period of less thanabout 1 minute in order to minimize or at least reduce the exposure tocellular damage.

It has been indicated that the skin patches or sheets which are normallytreated by the method and means of the present invention havesubstantial length and width dimensions. In this connection, referenceis being made to those sheets which are normally employed in thepractice at this time having dimensions of, for example, approximatelyinches X inches. It is this size of sheet which inhibits the passage ofthe contact fluid between mutually adjacent surfaces so as to preventrapid thawing, and thus exposing the structure to the risk of cellulardamage due to slow thaw.

It is sometimes desirable that the cellular skin patch or sheet beexposed to a cryophylactic or cryoprotectant agent. These agents are, ofcourse, commercially available and may be formulated from DMSO orglycerin. It will be appreciated that fresh frozen skin may be packagedwithout requiring acryophylactic or cryoprotectant agent, however theymay be used if deemed desirable, and the method and means of the presentinvention find utility in either instance.

We claim:

1. The method for preparing large cellular skin patches for preservationby cryogenic storage and subsequent thawing which comprises:

a. applying a woven scrim to one side of a large .patch of cellularskin, said scrim having a generally reticulate pattern of less thanabout 64 openings per square inch; and

b. cryogenically freezing said skin-scrim laminate.

2. The method as defined in claim 1 being particularly characterized inthat said woven scrim is adhesively bonded to one surface of said largecellular skin patch.

3. The method as defined in claim 1 being particularly characterized inthat said skin-scrim laminate is rolled into a cylindrical form prior tocryogenic freez- 4. The method as defined in claim 1 being particularlycharacterized in that said woven scrim is fabricated from fibersselected from the group consisting of nylon and polyethyleneterephthalate.

5. The method as defined in claim 1 being particularly characterized inthat said skin-scrim laminate is thawed by immersion in a reservoir ofnormal saline solution.

6. The method as defined in claim 1 being particularly characterized inthat said skin-scrim laminate is sterilized prior to freezing in anatmosphere of ethylene oxide.

2. The method as defined in claim 1 being particularly characterized inthat said woven scrim is adhesively bonded to one surface of said largecellular skin patch.
 3. The method as defined in claim 1 beingparticularly characterized in that said skin-scrim laminate is rolledinto a cylindrical form prior to cryogenic freezing.
 4. The method asdefined in claim 1 being particularly characterized in that said wovenscrim is fabricated from fibers selected from the group consisting ofnylon and polyethylene terephthalate.
 5. The method as defined in claim1 being particularly characterized in that said skin-scrim laminate isthawed by immersion in a reservoir of normal saline solution.
 6. Themethod as defined in claim 1 being particularly characterized in thatsaid skin-scrim laminate is sterilized prior to freezing in anatmosphere of ethylene oxide.